The transition from indirect band gap to direct band gap and effectively separating of electron-hole pairs in h-BC2N/MoSi2N4 heterojunction for photocatalytic water splitting

To improve the photocatalytic efficiency of MoSi2N4, we decided to use the organic material h-BC2N to form a new photocatalytic heterojunction, h-BC2N/MoSi2N4. Firstly, we calculated the phonon spectra of h-BC2N, MoSi2N4, and h-BC2N/MoSi2N4 heterojunction to determine their dynamical stability. Next, using the HSE06 density functional theory method, we calculated the band structures and DOS of h-BC2N, MoSi2N4, and h-BC2N/MoSi2N4 heterojunction to determine their band structures and types. To analyze the electron transfer in the h-BC2N/MoSi2N4 heterojunction, we calculated the work function and differential charge density to determine the direction of the built-in electric field and the electron transfer between h-BC2N and MoSi2N4. Furthermore, we discussed the interaction between h-BC2N and MoSi2N4, and the results showed that the VBM and CBM of h-BC2N and MoSi2N4 changed with the formation of the heterojunction. Then, we analyzed the reaction mechanism of the h-BC2N/MoSi2N4 heterojunction and found that the built-in electric field promotes the electron transition from the CBM of MoSi2N4 to the VBM of h-BC2N, effectively separating the photo-generated electron-hole pairs of MoSi2N4 in space, making h-BC2N/MoSi2N4 heterojunction a classical Type Z heterojunction. These results suggest that h-BC2N/MoSi2N4 heterojunction can improve the photocatalytic efficiency of MoSi2N4.